Jentschura, U. D., Milstein, A. I., Terekhov, I. S., Boie, H., Scheit, H., & Schwalm, D. (2008). Quasiclassical description of bremsstrahlung accompanying α decay including quadrupole radiation. Physical Review C-Nuclear Physics, 77(1): 014611. doi:10.1103/PhysRevC.77.014611.